Molecular sieve beads are used in many catalyst and adsorbent applications. However, methods used to produce beads have certain drawbacks. For example when spray-drying is used, a binder needs to be used to afford good strength which in turn dilutes the molecular sieve concentration. Pellet formation techniques also usually employ a binder and further have a minimum size limitation.
There are also a number of references in which catalyst particles are formed by depositing a layer onto an inner core. For example, U.S. Pat. No. 4,283,583 discloses a coated zeolite catalyst consisting of an inert core and an outer coating comprising an active catalytic zeolite material. The catalyst is prepared by wetting the inner core partially drying and then contacting the core with a zeolite powder. U.S. Pat. No. 4,482,774 discloses a composite zeolite having a crystalline silica polymorph as the core material and a modified silica overlayer which has substantially the same crystalline structure. The overlayer is formed by adding preformed particles of the silica core into a crystallization gel at crystallization conditions thereby crystallizing the zeolite onto the core. U.S. Pat. No. 4,088,605 discloses growing a substantially aluminum free shell onto an aluminum containing zeolite. U.S. Pat. No. 5,895,769 discloses depositing a polycrystalline zeolite onto a porous substrate. U.S. Pat. No. 5,935,889 discloses preparing catalyst particles by coating core particles with an atomized slurry containing a coating material. Finally, U.S. Pat. No. 6,013,851 discloses a core zeolite having deposited thereon a surface layer where the surface layer has a higher Si/Al ratio than the core.
Applicants have developed a unique process for preparing molecular sieve beads in which molecular sieve seeds or particles are slurried in a solution containing reactive sources of the framework elements of the molecular sieve. To this slurry there are added sources of the framework elements at a rate and for a time to form a gel and agglomerate the gel and particles into beads. The beads can be isolated and comprise a crystalline molecular sieve component and an amorphous component which is a precursor to a molecular sieve.